Method for producing fine monofilaments consisting of polypropylene, fine monofilaments consisting of polypropylene and the use thereof

ABSTRACT

In a process for producing fine monofilaments having improved abrasion resistance from a poly-propylene having a melt flow index (MFI) 230° C./2.16 kg  of 2-16 g/10 min at a linear density of 5-20 dtex (0.027 mm-0.053 mm), a compound consisting of 80 to 99.9% by weight of chips and 20 to 0.1% by weight of an additive is added to the extruder, the melt is spun at a speed of at least 1200 m/min, the fibre is cooled in an air bath at room temperature, supplementarily stretched at a temperature of 110-150° C. to a linear density of 5-20 dtex and wound up.  
     The monofilaments comprising a polypropylene having a melt flow index (MFI) 230° C./2.16 kg  of 2-16 g/10 min, having improved abrasion resistance, and a linear density of 5-20 dtex (0.027 mm-0.053 mm) and an abrasion resistance score ≦2. The monofilaments have a tenacity of at least 48 cN/tex and an elongation at break of less than 45% for a mechanical constant (constante méchanique) of at least 295 cN/tex and a specific work to break value of more than 61.5 cN·cm/dtex.  
     The fine monofilaments according to the invention are useful for producing woven screen fabrics for filtration and screen printing without abrasion deposits.

[0001] The invention relates to a process for producing finemonofilaments having improved abrasion resistance from polypropylenehaving a melt flow index (MFI)_(230° C./2.16 kg) of 2-16 g/10 min, to amonofilament of polypropylene having a melt flow index(MFI)_(230° C./2.16 kg) of 2-16 g/10 min having improved abrasionresistance and a linear density of 5-20 dtex (0.027 mm-0.053 mm) andalso to the use thereof.

[0002] Industrial fabrics composed of polypropylene are becoming ofincreased interest in the automotive industry, in particular becausethey are lighter and more stable to environmental effects and mechanicalstress than other thermoplastic materials. There is a particular demandfor fine monofilaments, which permit a further weight reduction. By finemonofilaments are meant monofilaments having a linear density of lessthan 30 dtex and especially less than 25 dtex.

[0003] However, monofilaments composed of polypropylene only have thedisadvantage of severe dusting in the weaving operation as a consequenceof the low abrasion resistance of pure polypropylene, although otherthermoplastics are known to have an abrasion problem too. For instance,EP-A2 0 784 107 mentions melt-spun polyamide, polyester andpolypropylene monofils and shows that abrasion-resistant filaments areobtained with 70-99% by weight of fibre-forming polymer and 1-30% byweight of a maleic anhydride modified polyethylene-polypropylene rubberand further additives. However, the examples are limited to nylon 6 andpolyethylene terephthalate and to a copolyamide of PA66 and PA6 asfibre-forming polymer. Spinning speeds are not reported. The relativelythick monofilaments exemplified are useful for papermachine wire fabricsand lawn mower wires. The production of relatively fine polypropylenemonofilaments is not disclosed.

[0004] EP-A-1059370 discloses a method for the production ofpolypropylene multifilaments for textile purposes. The starting materialused is a metallocene-catalysed isotactic polypropylene having a meltflow index of less than 25 g per 10 minutes in order that the desiredshrinkage properties may be achieved. Low-shrinkage filaments arepreferably produced using polypropylene chips having a high MFI value.The yarns produced are only described in general terms. Monofilamentsare not described at all.

[0005] EP-A-0028844 describes a textile multifil polypropylene filamentyarn. The starting polymer is a polypropylene having a melt flow indexbetween about 20 and 60. The problem of abrasion encountered in theprocessing of fine monofilaments was evidently not observed under thereported spinning and stretching conditions and in the course of thefurther processing.

[0006] It is an object of the present invention to provide an economicalprocess for producing fine abrasion-resistant monofilaments composed ofpolypropylene. It is a further object of the present invention toproduce polypropylene fine monofilaments having improved resistance toabrasion in weaving.

[0007] It is yet a further object of the present invention to providethe use of a fine monofilament having good abrasion resistance forproducing industrial fabrics.

[0008] These objects are achieved according to the invention when acompound consisting of 80 to 99.9% by weight of chips and 20 to 0.1% byweight of an additive is added to the extruder, the melt is spun at aspeed of at least 1200 m/min, the fibre is cooled in an air bath at roomtemperature, supplementarily stretched at a temperature of 110 to 150°C. to a linear density of 5-20 dtex (0.027 mm-0.053 mm) and wound up. Itis essential here that the additive has been thoroughly dispersed in thepolypropylene and that no difference is observable in the resultingmonofilament.

[0009] This is the first time that it has been possible to produce finepolypropylene monofilaments using a spinning speed of 1200 m/min. It hasbeen determined to be advantageous to use additives selected frommodified polyolefins and aliphatic diesters.

[0010] Particularly advantageous additives are modified polyolefins usedin an amount of 4.5 to 15% by weight, especially 6 to 13% by weight andpreferably 8 to 12% by weight of polypropylene/polyethylene having amelting point >140° C. A melting point of less than 140° C. isinconvenient to meter. This is because at temperatures below 140° C. thechips stick together in the extruder. Using less than 4.5% by weight andmore than 15% by weight of polypropylene/polyethylene makes for amonofilament having an unsatisfactory abrasion resistance. This variantsurprisingly requires no further additives to achieve outstandingabrasion resistance.

[0011] In a further variant, the additive used is advantageously 3-10%by weight, especially 3 to 7% by weight and preferably 3 to 6% by weightof an impact modifier. Useful impact modifiers do not soften at up to100° C. and are constructed of linear styrene-ethylene/butylene-styreneblock copolymers or alloys of linear styrene-ethylene/butylene-styreneblock copolymer//styrene-ethylene/butylene biblock.

[0012] In a further variant, the additive used is advantageously0.1-0.2% by weight of a plasticizer. Diisononyl adipate is a mostsuitable plasticizer.

[0013] In a further variant, the additive used is advantageously0.05-1.0% by weight and especially 0.3 to 1.0% by weight of a lubricant.Useful lubricants are particularly metal salts of carboxylic acids,linear or branched hydrocarbons, fluoroelastomers,polydimethyl-siloxanes.

[0014] In a further variant, it is advantageous to use fillers asadditive. Particularly useful fillers are 0.01-0.1% by weight ofAerosils and 0.1-1.0% by weight of calcium carbonate.

[0015] In a further variant, the additive is a compounded combination of2-10% by weight of an impact modifier, 0.1-0.2% by weight ofplasticizer, 0.01-0.1% by weight of Aerosil or 0.1-1.0% by weight ofcalcium carbonate as fillers, 0.05-1.0% by weight of lubricants and0.1-0.5% by weight of heat stabilizers. Useful heat stabilizers includesterically hindered phenols, phosphites and phosphonites.

[0016] The main polymer contemplated for the monofilaments according tothe invention is a polypropylene having a melt flow index(MFI)_(230° C./2.16 kg) of 2-16 g/10 min and a linear density of 5-20dtex (0.027 mm-0.053 mm). A melt flow index of less than 2 g/10 min hasthe disadvantage that the melt-spinning operation requires excessivelyhigh temperatures, which leads to destruction of the polymer. A meltflow index of more than 16 g/10 min has the disadvantage that theresulting abrasion resistance is inadequate. An abrasion resistancescore ≦2 is achieved by a monofilament which is easily weavable into atextile fabric and produces a surprising cleanness.

[0017] The monofilament according to the invention has a tenacity of atleast 47 cN/tex and an elongation at break of less than 45%.

[0018] The monofilament according to the invention has a mechanicalconstant (constante méchanique) of at least 285 cN/tex.

[0019] The invention will now be more particularly described by way ofexample.

EXAMPLE 1

[0020] Polymer

[0021] The fibre-forming monofilament used was in all runs apolypropylene having a melt flow index (MFI)_(230° C./2.16 kg) of 12.0g/10 min. For each run, 5 kg of polypropylene chips are blended usingtinplate cans and a tumble mixer. Three different blending methods wereused, depending on the additive. The individual methods are described inthe examples. The blend of chips and additive is directly introducedinto the extruder and melted.

[0022] Spinning Conditions

[0023] Extruder Diameter 38 mm:

[0024] Maximum p=100 bar

[0025] Throughput: 1-10 kg/h

[0026] 6 heatable zones

[0027] Spin pack: Diphyl-heated; 1 spinning position

[0028] Spin pump: 3-27 rpm

[0029] Spinnerets: diameter outer/inner=85/70 mm

[0030] Quench chimney: 450-1100 m³/h; 1=1.3 m

[0031] Extruder temperatures for zones 1 to 5: 180/230/250/250/265/275°C.

[0032] Pack+spinnerets: 275/275° C.

[0033] Throughput: 1.65 kg/h

[0034] Quench air: 700 m³/h

[0035] Melt temperature:=280° C.

[0036] Spinning take-off speed: 1200 m/min

[0037] Stretching Conditions

[0038] Stretching is carried out using a laboratory stretching rangeequipped with two stretching units each made up of a godet (=10 cm) anda separating roller.

[0039] The monofilaments undergoing a stretching operation pass throughthe following elements:

[0040] Yarn brake

[0041] Stretching unit V1, equipped with an additional feed or rubberroll. No snubbing pins.

[0042] Hotplate 20 cm in length and positioned 20 cm away from thestretching unit

[0043] Stretching unit V2

[0044] Traveller ring spindle

[0045] The variants are stretched using a stretch ratio of 3.6:1 and ahotplate (20 cm) at 130° C. The take-off speed of stretching unit V2 is514 m/min.

EXAMPLE 2 (RUNS 2-4)

[0046] In the case of the modified polyolefins, the chips blend,consisting of polypropylene and modified polyolefin, PP/PE meltingpoint >140° C., is mixed for one hour.

EXAMPLE 3 (RUNS 5-7)

[0047] In the case of the modified polyolefins, the chips blend,consisting of polypropylene and impact modifier, is mixed for one hour.It is advantageous to add an antistat, such as 0.1% of Atmer 110 (trademark of Uniqema) in the case of these blends.

EXAMPLE 4 (RUNS 8 AND 9)

[0048] The plasticizer is added to the polypropylene chips and mixed infor two hours.

EXAMPLE 5 (RUNS 10-12)

[0049] In the case of the pulverulent additives such as fillers,lubricants, heat stabilizers, etc., the chips are first tumbled for halfan hour with a coupling agent such as Basilon M100 (trade mark of BayerAG) before the remaining additives are added and mixed in for a furtherone and half hours. This series of runs includes the incorporation ofcalcium carbonate into polypropylene similarly to the above description.

EXAMPLE 6 (RUNS 13-16)

[0050] In this example, a lubricant is added to the polymer in variousamounts.

[0051] Same preparation as in Example 5.

EXAMPLE 7 (RUNS 17-19)

[0052] In the case of the additives in the form of a combination ofdifferent compounds, run 17 contains two different lubricants (0.2 and0.05%) and Aerosil at 0.05%. Runs 18+19 are based on three additives.

[0053] 0.35% of heat stabilizer, 0.3% of calcium carbonate and 0.15% oflubricant 4

[0054] 0.5% of heat stabilizer, 0.2% of lubricant 4 and 0.01% of Aerosil

[0055] Same preparation as in example 5.

[0056] The results are summarized in Table 1. TABLE 1 BreakingMechanical Specific work to Run ABTER Tenacity extension constant breaknumber ADDITIVE score dtex [cN/tex] [%] [cN/tex] [cN · cm/dtex] 1   0 49.9 51.4 32.6 293.47 61.4 2   5% 1.8 10.4 53.5 31.7 301.22 62.69 3   10%1.0 10.4 54.1 30.3 297.80 59.57 4   15% 2.0 10.8 53.3 30.6 294.84 59.205   3% 2.0 10.8 47.7 41.1 305.80 76.52 6  4.5% 0.8 10.4 48.9 42.9 320.2982.50 7  6.0% 0.8 10.4 48.4 41.1 308.78 77.07 8 0.10% 1.66 10.8 48.834.5 286.63 62.92 9 0.15% 10  0.4% 2.5 10.4 49.5 29.3 267.94 51.46 11 1.2% 0.83 11.2 47.2 43.4 310.95 81.67 12  2.0% 13  0.2% 3.66 10.1 50.531.8 284.78 58.53 14  0.5% 1.33 10.4 51.2 34.9 302.47 67.17 15  0.8%0.83 10.4 51.4 32.1 291.22 60.81 16  1.0% 1.16 10.4 51.9 30.3 285.6967.36 17 0.2/0.05/0.05% 0.83 10.4 51.6 34.1 301.32 65.65 180.35/0.3/0.15% 0.83 10.8 49.3 37.1 300.29 69.53 19 0.50/0.2/0.01% 1.1610.8 51.5 40.7 328.55 78.97

[0057] The results are illustrated in graphs.

[0058]FIG. 1 shows the abrasion behaviour as a function of the additionof an additive as per Example 2.

[0059]FIG. 2 shows the abrasion behaviour as a function of the additionof an additive as per Example 3.

[0060]FIG. 3 shows the abrasion behaviour as a function of the additionof an additive as per Example 6.

[0061]FIG. 1 shows the curve from the addition of a modifiedpolypropylene/polyethylene having a melting point of >140° C. as perExample 2. Without addition of an additive, the pure polypropyleneachieves an abrasion test score of 4, which indicates unsatisfactoryabrasion in the fabric. It is surprising that abrasion initiallyimproves with increasing amounts being added, up to an addition of 10%by weight, and deteriorates again at higher amounts added.

[0062]FIG. 2 shows the curve resulting from the addition of an impactmodifier. As the amount of additive increases, abrasion initiallydecreases, reaching a minimum at 5% by weight. Larger quantities produceno further benefit.

[0063]FIG. 3 shows the curve resulting from the addition of differentlubricants. Here, small amounts added initially achieve a markedimprovement in the abrasion behaviour. Raising the amounts added yieldsno further improvement in abrasion behaviour.

METHODS OF MEASUREMENT

[0064] melt flow index by ASTM D1238

[0065] abrasion test by ABTER

[0066] This test is a simple simulation of the weaving process on a testapparatus without weft insertion. The monofilaments are passed at aconstant speed through the most important elements of a weaving machinesuch as reed and healds while these are making their appropriatemovements. The monofilament speed is 9 m/h and the reed performs 525double strokes per minute.

[0067] The evaluation of the abrasion behaviour using the ABTER testeris carried out as follows.

[0068] the abrasion behaviour is tested on all monofils for a period of16 hours

[0069] the reeds are removed from the simulator and photographed

[0070] the deposits on the reeds are visually rated by three people, whoaward scores on a scale from 0-1 (=no deposit, no abrasion) to 5(=substantial deposit, substantial abrasion)

[0071] linear density determined in accordance with SN 197 012 and SN197 015 and additionally DIN 53 830

[0072] tensile tests to DIN 53 815, DIN 53 834 and additionally BISFA

[0073] the mechanical constant CM is calculated by the formula

CM={square root}D·F[cN/tex]

[0074] where D is the elongation at break in % and F is the tenacity incN/tex.

[0075] The fine monofilaments according to the invention are useful forproducing woven screen fabrics for filtration and screen printingwithout abrasion deposits.

1. Process for producing fine monofilaments having improved abrasionresistance from a polypropylene having a melt flow index(MFI)_(230° C./2.16 kg) of 2-16 g/10 min, characterized in that acompound consisting of 80-99.9% by weight of chips and 20 to 0.1% byweight of an additive is added to the extruder, the melt is spun at aspeed of at least 1200 m/min, the fibre is cooled in an air bath at roomtemperature, supplementarily stretched at a temperature of 110 to 150°C. to a linear density of 5-20 dtex (0.027 mm-0.053 mm) and wound up. 2.Process according to claim 1, characterized in that the additive used isselected from modified polyolefins and aliphatic diesters.
 3. Processaccording to claim 1, characterized in that the additive used is 4.5 to15% by weight of a polyolefin from polypropylene/polyethylene having amelting point >140° C.
 4. Process according to claim 1, characterized inthat the additive used is 3-10% by weight of an impact modifier. 5.Process according to claim 1, characterized in that the additive used is0.1-0.2% by weight of a plasticizer.
 6. Process according to claim 1,characterized in that the additive used is 0.05 to 1.0% by weight of alubricant.
 7. Process according to claim 1, characterized in that theadditive used is 0.01-1.0% by weight of fillers.
 8. Process according toclaim 1, characterized in that the additive used is a compoundedcombination of impact modifier, plasticizer, fillers, lubricants andheat stabilizers.
 9. Monofilaments comprising a polypropylene having amelt flow index (MFI)_(230° C./2.16 kg) of 2-16 g/10 min and havingimproved abrasion resistance, characterized by a linear density of 5-20dtex (0.027 mm-0.053 mm) and an abrasion resistance score ≦2. 10.Monofilaments according to claim 9, characterized by a tenacity of atleast 47 cN/tex and an elongation at break of less than 45%. 11.Monofilaments according to claims 9 and 10, characterized by amechanical constant (constants méchanique) of at least 285 cN/tex. 12.Monofilaments according to claims 9 to 11, characterized by a specificwork to break value of more than 61.5 cN·cm/dtex.
 13. Use of themonofilaments according to claims 9 to 12 for producing industrialfabrics.
 14. Use of the fabrics according to claim 13 as filtrationfabrics.
 15. Use of the fabrics according to claim 13 in screenprinting.